Forward osmosis membrane and method of preparing same

Abstract

The forward osmosis membrane and the preparation method thereof provided by the present invention, through fully cover the support mesh layer of the membrane with antibacterial nanoparticles, especially the mixture of nano-Ag and nano TiO2, ensures without reducing the strength, water flux and salt rejection, providing an effective, long-term and comprehensive antibacterial effect. In the present invention, the antibacterial nanoparticles, especially the mixture of nano-Ag and nano-TiO2, are used to carry out antibacterial modification on the support mesh of the forward osmosis membrane, so as to inhibit the growth of bacteria on the forward osmosis membrane, improves the forward osmosis and also improves the safety of the entire purification and filtration system. The antibacterial forward osmosis membrane of the present invention can be applied to the filtration and purification of complex water sources, especially the purification and filtration of eutrophic and bacteria-prone water sources.

What is claimed is: 
     
       1. A forward osmosis membrane, wherein the forward osmosis membrane has a sequentially stacked membrane structure, the stacked layer includes a hydrophilic support mesh and a hydrophilic polymer membrane layer, and the support mesh is non-woven or polyester screen modified by antibacterial nanoparticles; the antibacterial nanoparticle-modified support mesh is prepared by the following method: adding nano-Ag 0.1-0.5 wt. % (by weight) and nano TiO2 0.2-1 wt. % (by weight) into a 2-8 wt. % polyvinyl alcohol aqueous solution by weight, performing ultrasonic dispersion to obtain a modified suspension, immersing the polyester screen into the suspension, then obtained the antibacterial nanoparticle-modified support mesh by natural drying; the average particle size of the nano-Ag is 20 nm; the average particle size of nano-TiO2 is 5-10 nm;
 when using a 0.5 mol/L sodium chloride solution by volume as a draw solution, and using a 0.01 mol/L magnesium sulfate solution by volume as a feed solution, the membrane flux can reach 8-13 L/(m 2 *h), the rejection of the magnesium sulfate is above 97%, the antibacterial rate is above 90%, and the performances of the membrane is not affected even after 10 days of immersion in a eutrophication-rich raw water, after washing to test, its antibacterial capability is still above 90%. 
 
     
     
       2. The forward osmosis membrane of  claim 1 , wherein the mass ratio of nano-Ag and nano-TiO2 is: 1:2. 
     
     
       3. The forward osmosis membrane of  claim 1 , wherein the thickness of the support mesh is 30 μm-80 μm, the mesh size is 100 meshes-200 meshes; the thickness of the forward osmosis membrane is 50 μm-100 μm. 
     
     
       4. The forward osmosis membrane of  claim 3 , wherein the thickness of the support mesh is 30 μm or 50 μm or 70 μm, the mesh size is 100 meshes or 120 meshes or 150 meshes; the thickness of the forward osmosis membrane is 50 μm, 70 μm or 100 μm. 
     
     
       5. The forward osmosis membrane of  claim 1 , the hydrophilic polymer material is selected one of from the group consisting of polyacrylonitrile (PAN), polyacrylate (PA), polymethyl methacrylate, cellulose acetate, cellulose triacetate, polyvinyl alcohol, poly(ethylene oxide), polyvinyl acetate and combinations thereof. 
     
     
       6. A method of preparing for a forward osmosis membrane, comprising:
 (a) preparing an antibacterial modified support mesh: the support mesh is hydrophilic non-woven fabrics or polyester screens; the polyester mesh is modified by nano-Ag and nano-TiO 2 ; the method of preparing is adding nano-Ag 0.1-0.5 wt. % (by weight) and nano TiO2 0.2-1 wt. % (by weight) into a 2-8 wt. % polyvinyl alcohol aqueous solution by weight, performing ultrasonic dispersion to obtain a modified suspension, immersing the support mesh into the suspension, and then drying naturally; 
 (b) preparing a casting solution: adding hydrophilic polymers into a water-soluble solvent system mixing well to obtain the casting solution; 
 (c) coating the casting solution prepared in step (b) on the surface of a glass board covered with the antibacterial modified support mesh made at the step (a) to obtain an initial forward osmosis membrane with a certain thickness; 
 (d) treating an external layer of the initial forward osmosis membrane by removing the solvent, and forming a dense skin layer on the external layer to obtain a second initial forward osmosis membrane; 
 (e) performing phase separation film formation or interfacial film formation with the second initial forward osmosis membrane to obtain the forward osmosis membrane; 
 the average particle size of the nano-Ag is 20 nm; the average particle size of nano-TiO2 is 5-10 nm; 
 when using a 0.5 mol/L sodium chloride solution by volume as a draw solution, and using a 0.01 mol/L magnesium sulfate solution by volume as a feed solution, the membrane flux can reach 8-13 L/(m 2 *h), the rejection of the magnesium sulfate is above 97%, the antibacterial rate is above 90%, and the performances of the membrane is not affected even after 10 days of immersion in a eutrophication-rich raw water, after washing to test, its antibacterial capability is still above 90%. 
 
     
     
       7. The method of preparing for a forward osmosis membrane of  claim 6 ,
 wherein the thickness of the support mesh is 30 μm-80 μm, the mesh size is 100 meshes-200 meshes; the thickness of the forward osmosis membrane is 50 μm-100 μm. 
 
     
     
       8. The method of preparing for a forward osmosis membrane of  claim 7 ,
 wherein the thickness of the support mesh is 30 μm or 50 μm or 70 μm, the mesh size is 100 meshes or 120 meshes or 150 meshes; the thickness of the forward osmosis membrane is 50 μm, 70 μm or 100 μm. 
 
     
     
       9. The method of preparing for a forward osmosis membrane of  claim 6 ,
 wherein the hydrophilic polymer material is selected one of from the group consisting of polyacrylonitrile (PAN), polyacrylate (PA), polymethyl methacrylate, cellulose acetate, cellulose triacetate, polyvinyl alcohol, poly(ethylene oxide), polyvinyl acetate and combinations thereof. 
 
     
     
       10. The method of preparing for a forward osmosis membrane of  claim 6 , further comprising:
 (b-1) defoaming or removing bubbles from the casting solution prepared in the step (b); 
 the step (c) further including: coating the casting solution removed bubbles which prepared by step (b-1) on the surface of the glass plate covered by the modified antibacterial hydrophilic support mesh, using a film scraper machine to scrap to form the initial forward osmosis membrane with a certain thickness; 
 the treatment of the external layer and removal solvent in the step (d), including standing the initial forward osmosis membrane in the air to make the solvent volatilize and form the dense skin layer on the external layer; 
 in the step (e), through immersing the second initial forward osmosis membrane into a deionized water to make it gel and split phase to form a membrane; 
 (f) immersing the forward osmosis membrane obtained by step (e) into a deionized water to remove the residual organic solvent; 
 (g) taking out the forward osmosis membrane and rising it with a deionized water, and then saving it in a sodium metabisulfite solution for later use. 
 
     
     
       11. The method of preparing for a forward osmosis membrane of  claim 10 , wherein the thickness of the support mesh is 30 μm or 50 μm or 70 μm, the mesh size is 100 meshes or 120 meshes or 150 meshes; used after a pre-cleaning treatment, the pre-cleaning treatment comprises: soaking the polyester mesh respectively in a solution with 10% of sodium hydroxide by volume and a solution with 2% of hydrochloric acid by volume for one hour to remove impurities adsorbed on the surface and then rinsing with a deionized water, then drying for the next step use; the thickness of the initial forward osmotic membrane prepared by the film scraper machine is from 30 μm to 100 μm. 
     
     
       12. The method of preparing for a forward osmosis membrane of  claim 11 , wherein in the step (b), a mixing condition is to stir mixtures under a temperature of 30-50° C. for 12-48 hours to make the mixtures evenly mixed;
 the defoaming method is to keep standing in air for 12-36 hours to achieve fully defoaming or through an assistance of a ultrasonic to defoam; the condition of standing in air is under an environment not be higher than 25° C. temperature and not be lower than 90% humidity, the standing time is from 30 seconds to 90 seconds to form the dense skin layer; 
 in the step (f), before soaking the membrane into the deionized water, heat treating the membrane into a water bath at 40-50° C. water for 5-20 minutes; the soaking time in the deionized water is 12-36 hours to remove the residuals of the organic solvents; 
 in the step (g), the concentration of the sodium metabisulfite solution is between 0.5-2% by volume.